Engine compression brakes provide increased braking capability for heavy duty vehicles thereby decreasing stopping distances as opposed to those vehicles not having compression brakes. An engine compression brake is essentially an engine that, during operating conditions, is deprived of fuel and transformed momentarily into an air compressor. The deprivation of fuel to the engine produces additional drag on the power train and thus serves to supply additional braking capability over and above that available through the conventional vehicular braking system.
If an engine compression brake is included in a vehicle having sophisticated electronic control systems for control of clutch engagement, throttle position, gear shifting of a manual/automatic transmission and cruise control operation, certain operating conditions must be anticipated to prevent serious injury to the driver and persons within nearby vehicles. For example, during a normal, manual downshift process with the engine compression brakes activated, the engine compression brakes should be activated only when the control system senses the throttle lever is in a minimum engine speed position and the clutch is engaged (i.e., pedal out). Another example of an undesirable condition arises during an electronically controlled shift between two final drive gear ratios when the clutch pedal must be out and the throttle is electronically controlled by the control system. A typical engine compression brake controller of the prior art would activate the engine brake in response to the second set of conditions when an electronically controlled transmission gear shift operation is occurring.
Further difficulties encountered with electronic gear shifting occur if an electronic shift is unsuccessful and the transmission is placed in neutral. In addition, for an electronic control system to command the engine to synchronous rpm speeds during electronic controlled gear shifting, the engine brakes must be disabled else the engine is deprived of fuel.
Thus, a controller for monitoring operating conditions of a vehicle and disabling engine compression brake operation to prevent undesirable and hazardous results is needed for use with electronic vehicle control systems.